This invention relates generally to adjustable vehicle seats, and more particularly it relates to a motor vehicle seat having a supporting guide rail assembly including a stationary rail secured to the floor of the vehicle, a travel rail secured to the seat and being movably coupled to the stationary rail, a longitudinal position adjuster including a motor having a driving pinion, a drive gear engaging the travel rail and a rotary shaft driven by the pinion drive supporting for joint rotation with the drive gear.
In a known adjustable seat support of the above-described kind the travel rail which is connected to the seat part is provided with a gear rack which acts as the longitudinal position adjuster for the guide rail assembly. The drive gear is in mesh with the rack and the shaft is rotatably supported in a bearing plate which in turn is rigidly secured to the stationary rail. In most conventional position adjusters, the drive gear is the last stage of a reduction gear unit which is fixedly mounted on the bearing plate. The first stage of this reduction gear assembly is the pinion of a driving motor, usually an electromotor, and the second stage is usually a worm gear. The electromotor with its pinion and the reduction gear are constructed as a compact driving unit. The worm gear is preferably made of a self-lubricating synthetic material. In the case of a collision, however, the worm gear is subject to considerable acceleration forces which may cause breakage of the meshing teeth so that the vehicle seat may be thrown forwardly or rearwardly according to the direction of the impact, and consequently the danger of injury to the user of the seat is considerably increased.